Parasitic nematodes remain a major cause of morbidity and mortality to humans and livestock throughout the world. The burden of control falls mainly on chemotherapeutics but alarmingly, resistance to many anti-nematode drugs is becoming increasingly prevalent. There is pressing need for new drugs. FMRFamide-like peptides (FLPs) are a complex family of small, structurally-related invertebrate neuropeptides that are ubiquitous in the nervous systems of all nematodes. Most FLPs elicit remarkably potent effects on a range of nematode muscles, inducing profound contractions and relaxations at concentrations as low as 1 pM. Their distribution and physiological effects indicate FLPs are fundamental to the control of nematode locomotion, feeding and reproduction. Their receptors are therefore attractive novel drug targets. Recently, a number of G protein-coupled receptors (GPCRs) with FLP ligands have been identified in Caenorhabditis elegans. Here, it is proposed to use this information to identify FLP receptors in the parasitic nematode, Ascaris suum. The specific aims of the proposal are (1) to test the hypothesis that GPCRs with high homology to the C. elegans FLP receptors are expressed in A. suum and (2) to test the hypothesis that the ligands for these receptors are endogenous A. suum FLPs. Candidiate A. suum FLP receptors, identified from the Ascaris EST database through BLAST searches using the C. elegans sequences, will be fully characterized using RACE PCR. These receptors will be functionally expressed in a heterologous system and screened with known A. suum FLPs. FLP ligands will be identified using FLEXstation II (Molecular Devices) to monitor elevated intracellular calcium levels associated with receptor activation. Successful completion of this two-year project would produce structural and functional information on the first parasitic nematode neuropeptide receptor. It would facilitate further experiments to provide a better understanding of the biology of this important family of neurotransmitters in nematodes. It would also provide a substrate for drug development studies.